1. Field of the Invention
The invention relates to a method for authorizing in data transmission and communication systems.
2. Brief Description of the Background of the Invention Including Prior Art
It is known that in telebanking or in remote terminal banking the user requires in addition to his or her permanent password (personal identification number PIN) for each individual transaction additionally a transaction authorization number (TAN). Such transaction authorization numbers TANs are transmitted to the user in larger blocks by mail. Thus, there exists the risk that third persons receive knowledge of such transaction authorization numbers TANs and can perform a misuse in connection with the password. The risk is increased by such transaction authorization numbers TANs having a validity which is de facto unlimited in time.
Furthermore, call-back systems are known, wherein the called-in system assures based on a call-back at the generally stored telephone number that the calling system is authorized and that no foreign system pretends to be an authorized system. The disadvantage of the call-back systems comprises that an unauthorized user, who has procured a functional access to the authorized calling system from any possible source, can work without a problem based on this illegally obtained authorization, since the call-back system checks only whether the call-back system has been called by a system which is authorized in principle by a basically authorized system.